One of the options in the treatment of advance joint arthrosis is joint resurfacing, i.e. removing only the diseased or damaged surfaces of the head of the bone. In the United States, hip resurfacing was first approved by the FDA based on the Birmingham Hip Resurfacing (BHR) technology developed by Derek McMinn. The BHR has a mushroom shape with a metal cap for placement on the femur head which fits into a cup placed in the acetabulum. The cap is fixed onto the head of the femur by way of a very small stem which is introduced through the femur head (and neck)
Hip resurfacing or hip surface replacement has a number of advantages over classical hip replacement therapy. The main advantage of the bone conserving system of hip resurfacing is that femoral head and femoral canal can be preserved such that when a revision is required, there is still a complete femur bone left for a stem in case total replacement becomes necessary. Moreover, there is more chance that the natural gait is recovered and the stress is transferred in a natural way through the neck of the femur rather than immediately on the thigh (which often causes pain). Finally, as resurfacing devices can be made in metal or other wear-resistant material, the resurfaced hip has a low wear rate such that even a young patient will probably not outlive the implant. In most cases, bone head resurfacing will be preferable over procedures which involve total bone head replacement.
The satisfactory performance of a joint surface replacement device is determined not only by the design of the device itself, but also by the surgical positioning of the implanted component(s) and the proper fixation of the implant. Improper placement or positioning of the implant will not only result in a failure to restore the clinical bio-mechanics of the joint but will result in inadequate fixation of the implant to the bone. To ensure the correct installation of a new surface on the head with resurfacing device use is made of guiding tools which can ensure the appropriate position and orientation of cutting, drilling and preparation tools based on pre-operative planning of the surgical intervention.
A number of different alignment devices have been described in the art.
U.S. Pat. No. 4,860,735 discloses a drill alignment apparatus which is mounted on top of a drill handle and comprises an alignment rod and a clamp apparatus for fixing onto the bone. By placing the clamp on the bone, the drill handle can be moved only in the direction of the alignment rod. U.S. Pat. No. 5,312,409 discloses a drill alignment guide, which comprises a adjustable clamp assembly for clamping onto the bone connected by an L-shaped bar to a drill guide. Upon clamping of the device on the bone, the drill guide is positioned on the bone head. U.S. Pat. No. 4,896,663 discloses a femoral drill jig comprising a clamping mechanism which clamps on to the femoral neck and a head cone which comprising a guide bushing for guiding a drill into the femur head.
The above-described methods involve generic, adjustable devices that consist of a guiding element, an element that clasps around a part of the bone, and one or more arms connecting the two. These devices are often unstable as they do not fit perfectly on the patient's bone and and in some cases inaccurate because of the great distance between the supporting anatomy and the planned point of entry of the surgical instrument. Indeed, as a large part of the head of a limb bone is covered with cartilage, this surface is smooth and slippery which makes it less suitable as secure attachment point. In addition, the thickness of the cartilage may vary from patient to patient. Cartilage is very difficult to segment on CT-images and even using MRI implies an additional step which is time-consuming. Thus it is very difficult to design structures precisely fitting on to the bone head.
An increasing number of surgical interventions currently benefit from the use of medical-image-based models which can assist in precisely executing the pre-operative planning of the intervention. U.S. Pat. No. 5,768,134 describes methods for making a medical model using rapid prototyping which model can includes artificial elements which can be functional such as drill-guides or pins.
There is a need for surgical guides, which do not require excessive image analysis but nevertheless are stable and provide the ability to accurately and efficiently insert or contact a surgical instrument into or with the head of a patient's limb bone.